The invention concerns a platform lift, especially for transferring wheelchair occupants between a passenger compartment and the ground. The inventive lift has a particular configuration for parallelogram-linked support arms driven using a drive cylinder, and includes safety gates that are mechanically linked to operation of the lift.
In a preferred arrangement the lift mechanism has movable parts successively connected on different axes to permit rotation about the respective axes for stowing, deploying and moving a platform that supports the load, such as a wheelchair. The lift is apt for use in a van, bus or light truck.
The platform for the wheelchair or other load is pivotable on a horizontal axis between a horizontal supporting orientation and a vertical stowing orientation. In a preferred arrangement, the horizontal axis on which the platform pivots is in turn mounted so as to pivot on a vertical axis at one lateral side of the door, whereby the platform when oriented in a vertical position can be opened and closed like a door or gate panel.
The horizontal axis hinging is between the platform and a base plate. At one side of the doorway the baseplate is carried on a heavy duty vertical hinge axis coupling or journal post, and at the opposite side a protruding end of the baseplate is fixed with a clamping latch.
The horizontal axis pivoting between supporting and stowed positions and the vertical axis gate-like pivoting are between the platform part and two vertical standards that extend vertically and are disposed at the lateral opposite sides of the doorway. The vertical standards are mounted by a parallelogram linkage to vertical posts that are rigidly fixed to the vehicle at the lateral sides of the doorway.
The lift has at least three distinct modes of movement. In one mode, the parallelogram linkage holds the platform in a horizontal orientation as the platform is raised or lowered between ground level and the level of the vehicle passenger compartment. Movable gates at the platform edges permit the wheelchair to roll onto and off of the platform at either level and block roll-off when the wheelchair is between levels.
In a second mode, the platform is pivotable on a horizontal axis relative to the vertical standards. The platform is pivoted on the horizontal axis to raise the platform from its horizontal wheelchair-carrying orientation to a vertical stowed orientation.
A third mode is gate-like hinging to block or clear the doorway. With the platform vertical, and preferably with the vertical standards retracted via the parallelogram linkage, the platform and its base plate can be detached from one vertical standard to hinge on the vertical axis defined by the journal post at the other vertical standard, so as to hinge open and closed like a door or gate.
According to an inventive aspect, movable doorway plane barriers are linked between the relatively movable parts of the lift and are structured for automatic deployment when the platform is in a position other than coplanar with the passenger compartment. The barriers are linked with a sort of lost motion engagement rather than a positive engagement so that the barriers are compliant should they deploy onto an obstruction such as a person occupying the space. The barrier member is mechanically coupled to the movable parts of the lift by a mechanism having a lost motion component. The barrier member is deployed into position obstructing the doorway immediately upon displacement of the lift from a fully retracted position, wherein the barrier member is against a stop. On further displacement of the lift, the lost motion allows the barrier member to remain stationary as the lift is lowered. Moreover, the lost motion can be compliant if the barrier member is arrested short of its stop, for example if the barrier member is deployed against a person or an object in the doorway.
The movable vertical standards are connected to the fixed posts by a set of parallelogram arms. A drive means is provided such as a drive cylinder that is controllably extensible and retractable, e.g., a hydraulic or pneumatic cylinder, linear actuator motor or the like, for expanding or contracting the parallelogram linkage. According to an inventive aspect, the drive cylinder is mounted so as to have one or both of its opposite ends attached at rotational pivot points spaced from the pivot points that attach the parallelogram members. This arrangement has a number of advantages including the ability to orient the cylinder for urging in the vertical standards to nest of couple into the fixed posts, and a wear resistance aspect.
When nested together, the movable vertical standards engage with the fixed posts at engagement couplings, locking to provide a stable structure from which the platform can hinge on the journal post, without sagging.
A particularly robust and secure clamped latch arrangement is provided between the platform and the adjacent movable vertical standard on the side opposite from the vertical hinge. The clamped latch comprises a leveraged operator that fixes a protruding bar adjacent to the horizontal pivot axis of the platform, received in a structurally supportive receptacle coupled to the vertical movable frame. The journal post and clamping latch bear the concentrated load of a wheel chair on the platform when cantilevered outwardly.
Platform lifts with parallelogram linkage supports are disclosed, for example, in U.S. Pat. No. 4,456,421xe2x80x94Robson; U.S. Pat. No. 4,534,450xe2x80x94Savaria; U.S. Pat. No. 4,984,955xe2x80x94McCullough; U.S. Pat. No. 4,808,056xe2x80x94Oshima; U.S. Pat. No. 5,234,311xe2x80x94Loduha, Jr. et al.; U.S. Pat. No. 5,261,779xe2x80x94Goodrich; and, U.S. Pat. No. 5,806,632xe2x80x94Budd et al., which are hereby incorporated. These patents disclose a number of alternative arrangements in which a load platform is carried by a movable member of a linkage structure having paired opposite members. Typically the opposite members are straight bars coupled to hinge or pivot at points near their ends.
A proximal one of the members is defined by or is rigidly attached to a portion of a vehicle at a doorway. The parallelogram linkage expands and contracts to move a load platform carried by a distal one of the members, back and forth between the ground level and the vehicle passenger compartment level. The members of the linkage need not be straight or elongated members. The pivots need not be located at the ends of the members. However, the members maintain a rigid space between hinge points that define the apices of a parallelogram. The parallelogram can expand into a rectangle where the lines connecting the pivot points are oriented at right angles at each of the four pivot points. The rectangle also can contract or collapse such that each pair of opposite angles becomes acute, with the other pair being obtuse. Assuming that there are no other impediments, the rectangle can collapse in either direction from a right angle. That is, either of the opposite pairs can become acute or obtuse.
A parallelogram linkage is advantageous in a load platform lift, for example for a wheelchair, because the linkage ensures that the opposite members of the linkage remain parallel. Thus if a proximal linkage member is vertical, for example being fixed at a vertical orientation in a vehicle doorway, the opposite member will also be vertical, at all positions of the parallelogram linkage. A load carrying platform can be arranged to be held horizontal on a linkage member that is opposite from the stationary linkage member of the parallelogram, and will remain horizontal as the lift moves.
Expansion and contraction of the parallelogram causes the lift platform to be raised and lowered. Typically, expansion from an upwardly collapsed position moves the platform outward and down. The linkage passes through an intermediate position at which the linkages are at right angles. Further downward movement of the platform carries the linkage into a downward and inward.
Driving forces can be coupled to the members of the parallelogram linkage in various ways. The parallelogram link members are structurally constrained by their connection to move only by expansion and collapse of the parallelogram. Any forces exerted in the required directions on the linkage members, or between the linkage members, may tend to expand or contract the members and thereby lift or lower the platform. However there are implications to driving the lift in one way or another.
It is possible to raise the lift, for example, by exerting a vertical force on any of the movable members at any point spaced from the stationary member. A chain or pulley arrangement with a flexible chain or belt can be connected between a parallelogram member and some higher point on the vehicle. Such a drive chain or pulley might not be the best choice for reasons of compactness, safety, mechanical advantage, cleanliness and other considerations. A drive cylinder is a neater and more compact alternative. However a drive cylinder or other driving device needs to develop the necessary force and to be connected to the linkage so as to provide the necessary leverage or mechanical advantage over the necessary length of stroke to move the lift between the passenger compartment and the ground. The traverse also needs to be accomplished in a reasonable time.
It may be preferable to have a moderate stroke rather than a very long or very short stroke, for reasons of expense. The drive cylinder can be expected to cycle numerous times during the life of the lift, and advantageously is durable and resistant to wear. A user has more confidence in a heavy duty lift structure than a light or wobbly one. Any looseness in the mechanical parts and in the operation of the drive causes shaking and a lack of security that is disturbing or possibly dangerous for persons using the lift. There are various ways in which lifts are designed to address problems associated with these and other aspects of structure, performance, longevity, expense, etc.
An example of some of the conflicts encountered in this design dilemma is shown by U.S. Pat. No. 5,261,779xe2x80x94Goodrich, which discloses an exemplary platform lift powered by an extensible drive cylinder and compares it to other lifts. The proximal member of the parallelogram is fixed to the vehicle so as to define two pivot points on a line that is inclined backward and upwardly relative to the plane of the doorway. Such an inclination has the result that if the parallelogram can be completely collapsed flat when the lift is raised, the linkage members will be disposed inwardly of the vehicle doorway. Another result, however, is that the drive cylinder needs to expand the parallelogram from its collapsed position to reach a point at which the platform is coplanar with the vehicle compartment floor, which point is then at an intermediate point along the arc traversed by the platform. The cylinder then needs to resist the force of gravity that operates to lower the lift. The cylinder has to operate in the opposite sense in raising the lift and finally stowing it within the passenger compartment.
The opposite members of the Goodrich linkage define a parallelogram in general, but the distance between the pivot points is not precisely equal on the opposite sides. As a result, there is a difference in the inclination of the platform between its raised and lowered positions. Specifically, when raised to the passenger compartment level, the platform slopes backward slightly, i.e., downwardly into the vehicle. When lowered to the ground, the platform slopes outwardly, i.e., downwardly toward the ground unless otherwise supported on the ground terrain. This sloping discourages accidental movement of a wheelchair onto the lift because such movement is uphill but is less positive than a barrier. The arrangement of the lift linkage members and the drive cylinder also has other implications.
Barriers are known for the purpose of preventing a wheelchair from rolling out of the vehicle department at an inappropriate point in the traverse of the wheelchair, namely when the platform is not coplanar with the floor of the passenger compartment. However such barriers need to be deployed whenever the platform is not located exactly and fully at this upward loading/unloading position. A barrier cannot be mechanically coupled to cycle together with the cycle of the lift, because the barrier would be only half deployed when the lift was halfway lowered, etc.
Lifts driven by drive cylinders (whether extended under power or retracted or both) require that the drive cylinder be attached pivotally at its opposite ends to some point on the parallelogram linkage members. The orientation of the drive cylinder relative to the parallelogram members changes as the lift traverses its arc. In Goodrich and in other similar lifts, the drive cylinder is coupled at its ends to the same pivot shafts at which the parallelogram members are also pivoted. This connection of the drive cylinder may seems appropriate, but according to the present invention a number of advantages are obtained by an improved arrangement for the parallelogram linkage members, the drive cylinder and the associated barriers.
It is an object of the invention to provide an optimized platform lift with a parallelogram mounting, for raising and lowering a load such as a wheelchair, between a ground level and a vehicle passenger compartment level.
A wheelchair lift is provided wherein a fixed posts and movable standards define opposite substantially-vertical parts of a parallelogram linkage coupled at four pivot points by parallel rotating arms, and the drive for the lift comprises an extensible cylinder mounted to apply force between points that are spaced from the pivot points between the arms and the vertical parts, at least on one end and preferably on both ends.
The drive cylinder has independent pivoting shafts at points of attachment located between the pivoting shafts coupling the parallelogram arms. The relative angle between the pivot attachments of the drive cylinder, versus the angle between the pivot attachments of the parallelogram members, is chosen to provide a particular combination of mechanical advantage and cylinder stroke length. This arrangement also has other advantages. For example the force and wear associated with the drive cylinder is borne by different pivot shafts (on one or preferably on both ends) than the pivot shafts forming the parallelogram linkage supporting the lift. Wear is substantially reduced.
The drive cylinder is inclined by an acute angle relative to the parallelogram arms. This enables operation with a moderate stroke and allows the cylinder to lift or lower the platform. When the lift is stowed in its upmost position, the parallelogram can be substantially collapsed flat, without requiring a corresponding accommodation for a particularly short drive cylinder. The drive cylinder in this collapsed position tends to pull and hold the parallelogram members securely collapsed, preventing vibration, and to pull the outer vertical standards into a nesting or coupling engagement with the fixed posts. In a preferred arrangement, the fixed posts in the vehicle doorway and the movable vertical standards carrying the platform, are provided with complementary male/female engagement structures that come into engagement when the parallelogram is collapsed. Thus the drive cylinder is arranged to pull these engagement structures together.
The preferred arrangement is substantially balanced by aligning the pivot points on the proximal vertical posts such that the pivot points of the parallelogram on the proximal side are on a line that is only slightly inclined inwardly toward the vehicle. Thus the vertical loading of the platform in the stowed position is minimal. When the platform is lowered for use vertical loading is increased. The platform cycles downwardly from the passenger compartment to the ground due to from gravity, extending the drive cylinder from a minimum length as stowed to a maximum length at the ground position. A variable choke valve can be provided to adjust the speed at which the lift falls due to gravity.
It is a further object of the invention to provide roll-off prevention barriers for the vehicle passenger compartment, associated with the lift, and operated by a mechanical linkage coupled to the lift. According to an inventive aspect, the barriers comprise pivoting gate members that rotate across the space between the fixed posts. According to an inventive aspect, the barriers are coupled with certain lost motion components such that the barriers deploy fully at the very beginning of the lift stroke. Although the lift has a relatively long stroke between its upper and lower extremes, the barriers are deployed immediately upon displacement of the lift platform from its uppermost position abutting the passenger compartment. According to another inventive aspect, the lost motion in the barrier couplings also permits the lift to proceed when the barriers are blocked, for example if the barriers deploy against an obstruction or onto a vehicle occupant located in the doorway.
According to additional aspects, the invention preferably has plural successive or parallel mounting aspects, operable independently, between the fixed posts and the load-carrying platform. On the load side, the platform pivots up for stowing or down for use. On the vehicle side, the posts are rigidly fixed at the lateral sides of the doorway. The posts and the vertical standards preferably nest together at male/female couplings, for example adjacent to each of the four corners of the doorway, which holds the vertical standards steady when the lift is retracted. The base member carrying the load platform horizontal pivot axis can be disengaged from one vertical standard to hinge on a journal post in the other vertical standard, permitting gate-like hinging to clear the doorway, preferably when the platform is rotated up from its horizontal load-carrying position into a vertical stowed position.
These aspects and objects are accomplished by a wheelchair lift according to the invention, to be mounted in a vehicle doorway at a passenger compartment. The platform part of the wheelchair lift can be raised and lowered around a horizontal pivot axis, into a stowed vertical position, and in that position can be rotated around the vertical hinge axis to clear the vehicle doorway for normal access without climbing over the platform.
A mounting structure having laterally-spaced fixed vertical posts is rigidly mounted in the vehicle doorway, inside the innermost (closed) position of the vehicle door. The mounting structure comprises vertical posts, preferably extending from the floor to the roof, with an upper header beam and a lower horizontal base member that frame the doorway together with the posts. Laterally spaced vertical movable standards are attached to the fixed posts by parallelogram linkages or arms and reside against the fixed posts in the retracted position of the lift. In the retracted position, complementary engagement structures engage between the vertical standards and the fixed posts. The engagement structures bear a lateral component of the load, and serve to position and align the vertical standards relative to the fixed posts. The engagement structures also define a stop position of the movable vertical standards as they are retracted against the fixed posts.
The drive for lifting and lowering the vertical standards relative to the posts comprises an extensible cylinder, preferably a cylinder on each side, attached at opposite ends between the fixed posts and the movable standards that are carried on the fixed posts by the parallel arms of a parallelogram linkage between the posts and vertical standards. The two parallelogram arms (preferably two on each side of the lift) comprise rigid members extending between pivot points on the posts and standards, respectively. The four pivot points form a parallelogram that expands and contracts for different positions of the lift.
According to an inventive aspect, the drive cylinder is attached at pivot points on the posts and standards that are between and spaced from the parallelogram pivot points. The cylinder is inclined relative to a line between the pivots mounting the parallelogram arms, which determines the mechanical advantage available to the cylinder and the length of its stroke during cycling of the lift.
The wheelchair supporting platform has at least three distinct modes of movement that can be effected sequentially for transferring a load in one direction or the other between the passenger compartment and the ground, or alternatively for clearing the doorway when the platform is stowed and not being used to carry a load. The platform is carried on parallelogram linkages holding the platform horizontal (when deployed) as the platform is raised or lowered between ground level and the level of the vehicle passenger compartment in one mode of movement. Preferably, this mode of movement is hydraulically powered. The hydraulic power can be adjustable, for example using an adjustable throttle valve between a hydraulic cylinder and a fluid pump or a fluid sump (or both), to adjust the speed at which the lift is raised or lowered, respectively.
The parallelogram linkages comprise at least two pivot arms attached at vertically spaced horizontal axis pivot points, between the fixed vertical posts and the movable vertical standards. The pivot arms and the posts and standards form a parallelogram between the pivot points. The parallelogram expands and collapses while moving the vertical standards and the platform it carries, through an arc around the pivot points on the fixed posts. The arc has a vertical span sufficient to move the load platform between the level of the passenger compartment and the ground adjacent to the vehicle, e.g. to a curb or to the street.
The specific layout of the parallelogram linkage and its dimensions relative to the vehicle are subject to variations, as shown in the prior art mentioned above, which is hereby incorporated. For example, the stowed position of the platform can be near top-dead-center on the arc, whereby the initial downward motion of the platform (or the final upward motion) is actually along a horizontal tangent. Preferably, the stowed position is slightly inward of top-dead-center, due to placing the pivot points on the fixed vertical posts on an inwardly inclined line so as to partly balance the weight of the lift when stowed. The weight of the platform is sufficient to balance the weight toward downward and outward movement, particularly when the platform is rotated from a vertical stowed position to a horizontal load bearing position.
According to an inventive aspect, however, the drive cylinder that drives and controls the motion of the lift is mounted in a particular arrangement wherein the force exerted by the cylinder is between pivot connections on the posts and standards along a line that is inclined relative to the parallelogram arms.
Due to the parallelogram mechanical connections, the standards remain parallel to the fixed posts. The parallelogram defined by the linkage collapses flat when the standards are retracted inboard toward the posts and expands when the standards are deployed outwardly and downwardly to lower the lift. The load supporting platform is pivotable on a horizontal axis on the inboard side of the lift to permit the platform to be raised from a horizontal wheelchair carrying orientation to a vertical stored orientation (defining the second mode of movement
For horizontal axis pivoting the platform is attached to the movable vertical standards on a horizontal hinge axis coupled to one of the vertical standards on a vertical axis journal post. On the side opposite from the journal post, a clamping latch attaches the opposite end of the horizontal hinge axis structure to the other vertical standard, bearing part of the load on the platform. Thus the platform can be pivoted into a vertical position where the platform is substantially in the plane of the standards. The standards are retractable via the parallelogram linkage back toward the posts that are rigidly attached to the vehicle on lateral sides of the doorway, thus collapsing the thickness of the overall mechanism.
Pivoting of the platform on its horizontal axis can be permitted or prevented by means of a latch for locking the platform against the standards, in an embodiment wherein the horizontal pivoting is not powered. Preferably, however, pivoting of the platform is driven in either direction by an linear actuator such that the gate is not dropped suddenly when deployed and can be pivoted into the stowed vertical position without manual assistance. A latch is not necessary in the embodiment in which the horizontal pivot is powered.
A front roll-off gate and a rear roll-off gate can be associated with the platform. These respective gates deploy or are retracted due to contact between the platform and the vehicle (when the lift is raised to the passenger compartment) or between the platform and the ground (when the lift is lowered). The gates prevent rolling onto or off of the lift when the lift is at any other elevation.
Both the lost motion doorway barriers and side handrail members are mechanically linked to the respective parts for automatic deployment and retraction as a function of the relative positions of the parts. The handrail members are pivoted via a connecting rod relative to the horizontal axis of the platform. When the platform is parallel to the standards (i.e., vertical) the handrail members collapse between the platform and the standards, and when the platform is moved perpendicular to the standards (i.e., horizontal), the connecting rod raises the handrail members to a position perpendicular to the platform.
The doorway barriers are movably mounted to the posts of the fixed frame in the doorway to block passage by protruding into the doorway opening when the platform has moved away from the doorway sill by operation of the parallelogram linkage. One or more barrier members (preferably one on each lateral side) is coupled at a fixed post to a pivot pin or axis oriented parallel to the extension direction of the parallelogram linkage, and thus operable to guide the barrier gate(s) to a blocking position spanning the doorway or to rotate back around the pivot pin to a retracted position at the fixed posts or behind the fixed posts relative to the doorway opening. This motion is driven by connecting links coupled to the movable parallelogram linkage. A driving linkage is coupled between the barriers and the parallelogram linkage, such as a simple bell crank linkage.
The barrier gates move from their retracted position to their extended or blocking position immediately upon commencement of expansion of the parallelogram linkage from the upward position of the lift. In their extended or blocking position the barrier gates rest against limiting pins that are fixed relative to the fixed posts and define the limit of rotation of the barrier gates around the pivot pins. At this limit of rotation the barrier gates preferably extend substantially horizontally across at least part of the width of the doorway opening, and at an elevation high enough to block a wheelchair from rolling through the doorway. The barrier gates occupy their blocking position when the platform is not abutting or very nearly abutting against the sill.
The barrier members are operated by couplings connected to other movable parts of the device, in particular to the parallelogram link members. The couplings are arranged to provide the correct leverage or mechanical advantage to move the barrier gates into their blocking position immediately after the platform begins to move away from the sill. As the couplings continue to advance with movement of the platform toward the ground, the barrier members are displaced relative to the coupling that drives them, over a span of lost motion. Additionally, the barrier members are attached to the couplings through at least one spring, such that the barriers can be displaced safely through the span of lost motion and against the bias of the spring, if the advancing barrier members encounter an obstruction when moving into the blocking position.
Each barrier gate can have a hub mounted on a pivot pin fixed to the gate-like frame members, and around which the barrier gate and the hub rotate. The hub has a bell crank arrangement or eccentric coupling fixed to the associated movable member of the parallelogram linkage so as to transfer linear motion of the movable member to rotation of the hub on the pivot pin. The barrier gate is also rotatable on the pivot pin but is attached to the hub by a spring such as a helical spring. A stop spaced from the pivot pin defines the limit of advance of the barrier gate. The bell crank coupling rotates the hub as the platform moves away from the sill, thus moving the barrier gate by its spring connection with the hub, from a retracted position to an advanced position against the stop. As the platform moves further toward the ground, the hub continues to rotate but the barrier gate remains against the stop over the span of lost motion. Over the span of lost motion, the spring is displaced (e.g., the helical spring is wound more tightly). When the platform is later moved from the ground toward the doorway sill, the barrier gate remains in the blocking position against the stop (unwinding the spring) for the initial one-third of the up-cycle, whereupon the barrier is rotated around the pivot pin by its spring connection with the hub, and moved back into the retracted position for the remaining two-thirds of the up-cycle.
A number of variations are possible and will be apparent from the following discussion of practical examples and preferred embodiments as illustrated in the drawings.